The present invention relates generally to derivatization and patterning of surfaces and more particularly to the formation of self-assembled molecular monolayers on surfaces using microcontact printing, derivative articles produced thereby, and novel optical elements.
In fields involving microelectronic devices, sensors, and optical elements, the development of devices that are small relative to the state of the art, controllable, and conveniently and relatively inexpensively reproduced with a relatively low failure rate is important.
A well-known method of production of such devices is photolithography. According to this technique, a negative or positive resist (photoresist) is coated onto the exposed surface of a material. The resist then is irradiated in a predetermined pattern, and irradiated (positive resist) or nonirradiated (negative resist) portions of the resist are washed from the surface to produce a predetermined pattern of resist on the surface. This is followed by one or more procedures. For example, the resist may serve as a mask in an etching process in which areas of the material not the substrate. According to another example, the patterned surface is exposed to a plating medium or to metal deposition under vacuum, followed by removal of resist, resulting in a predetermined plated pattern on the surface of the material. In addition to photolithography, x-ray and electron-beam lithography have found analogous use.
While the above-described irradiative lithographic methods may be advantageous in many circumstances, all require relatively sophisticated and expensive apparatus to reproduce a particular pattern on a plurality of substrates, and are relatively time-consuming. Additionally, no method of patterning nonplanar surfaces is commonly available according to these methods. In the field of electronic circuitry, an attempt is often made to save space by stacking planar circuit boards or chips, the boards or chips interconnected with auxiliary contacts. Alternately, a board or chip may be bent or otherwise formed in a nonplanar manner so as to save space, auxiliary contacts connecting components on different sides of the bend. All too often these auxiliary contacts are the cause of circuitry failure, and the attempt to move from the two-dimensional domain to a three-dimensional domain fails. Irradiative lithography provides no remedy to this complication, nor does it provide a method of conveniently and inexpensively reproducing an existing microelectronic circuit pattern, or the surface morphological features of other objects of interest.
Additionally, the above-described irradiative techniques are generally not amenable to the patterning of biological species such as proteins, as they typically utilize resists and solvents that are toxic to many biological species.
A need exists in the art for a convenient, inexpensive, and reproducible method of plating or etching a surface according to a predetermined pattern. The method would ideally find use on planar or nonplanar surfaces, and would result in patterns having features in the micron and submicron domain. Additionally, the method would ideally provide for convenient reproduction of existing patterns. Additionally, a need exists for the fabrication of surfaces that can pattern portions amenable to attachment of biological species, such as antibodies, antigens, proteins, cells, etc., on the micrometer scale.
The study of self-assembled monolayers (SAMs) is an area of significant scientific research. Such monolayers are typically formed of molecules each having a functional group that selectively attaches to a particular surface, the remainder of each molecule interacting with neighboring molecules in the monolayer to form a relatively ordered array. Such SAMs have been formed on a variety of substrates including metals, silicon dioxide, gallium arsenide, and others. SAMs have been applied to surfaces in predetermined patterns in a variety of ways including simple flooding of a surface and more sophisticated methods such as irradiative patterning.
Accordingly, a general purpose of the present invention is to solve problems associated with expense, complicated apparatus, and other complications associated with patterning surfaces for electronic, chemical, biological, and optical devices. One object is to provide a method of conveniently and reproducibly producing a variety of SAM patterns on planar and nonplanar surfaces, the patterns having resolution in the submicron domain, and being amenable to plating, etc. Another purpose of the invention is to facilitate the attachment of biomolecules on the submicron scale without loss of biological function. Another purpose of the invention is to provide a method of forming a template from an existing pattern having micron or submicron-domain features, the template conveniently reproducing the preexisting pattern.
Another general purpose of the invention is to provide optical elements and devices that are conveniently and inexpensively manufactured, and that are adaptable to a variety of systems.
The present invention provides a method of etching an article that is coated with a thin layer of resist. The method involves contacting a first portion of the resist surface with a stamp to transfer to the first portion a self-assembled monolayer of a molecular species in a first pattern. The self-assembled monolayer is contiguous with an exposed portion of the resist surface in a second pattern. The resist is removed from the surface of the article, according to the second pattern, by contacting the exposed portion of the resist surface with a first etchant that reacts chemically with the resist and that is inert with respect to the self-assembled monolayer. This exposes the surface of the article in the second pattern. A second etchant is applied to the exposed surface of the article that reacts chemically with the article and that is inert with respect to the resist. According to one aspect the resist is an electrical conductor. According to another, the resist is a metal oxide, and can be an oxide of the article. The article can be a semiconductor such as silicon gallium arsenide, or the like, and can have a nonplanar surface.
According to one embodiment, the self-assembled monolayer exposes a chemical functionality in the first pattern, and prior to the removing the resist, the molecular species is coated with a protecting species that is compatible with the chemical functionality and incompatible with the first etchant.
The present invention provides also a method of etching an article involving contacting a first portion of the surface of the article with a stamp to transfer to the first portion a self-assembled monolayer of a molecular species in a first pattern, the self-assembled monolayer being contiguous with an exposed portion of the surface in a second pattern and exposing a chemical functionality. A protecting species that is compatible with the chemical functionality is applied to the self-assembled monolayer, and the exposed portion of the surface is contacted with an etchant that reacts chemically with the resist and that is incompatible with the protecting species. According to another embodiment, the self-assembled monolayer exposes a chemical functionality, in the first pattern, that is less compatible with the protecting species than is the surface of the article that remains uncovered with the self-assembled monolayer. In this embodiment, the protecting species is positioned on the surface at regions not covered by the self-assembled monolayer and, when the etchant is applied, the etchant etches the article at regions not covered by the protecting species (including those regions originally covered by the self-assembled monolayer).
The present invention provides also a method of applying to a surface of an article a self-assembled monolayer of a molecular species. The method involves coating a portion of a stamping surface of a stamp with a self-assembled monolayer-forming molecular species, and transferring from the stamping surface to a first portion of the article surface the molecular species, while applying to a second portion of the article surface contiguous with the first portion a species that is not compatible with the molecular species. According to one aspect the method involves allowing the molecular species to spread evenly from the first portion of the article surface to the second portion of the article surface. According to another aspect the first portion of the article surface includes at least two isolated regions separated by the second portion, and the method involves transferring the molecular species from the stamping surface to the at least two isolated regions of the first portion, while applying to a second portion the species that is not compatible with the molecular species. The molecular species is allowed to spread from each of the at least two isolated regions of the first portion toward each other. The molecular species can be lipophilic and the species that is not compatible with the molecular species hydrophilic, or vice versa, and the article surface can be nonplanar. Prior to or during the transferring step the stamp can be deformed.
The present invention also provides a method involving applying to a surface of an article a first region and a second region of a self-assembled monolayer, where the first and the second regions are separated from each other by an intervening region. A species that is incompatible with the molecular species that forms the self-assembled monolayer is applied to the intervening region, and the molecular species is allowed to spread evenly from the first region toward the second region and from the second region toward the first region.
The present invention also provides a method of applying to a surface of an article a self-assembled monolayer of a molecular species. The method involves coating a portion of a stamping surface of a flexible stamp with a self-assembled monolayer-forming molecular species, deforming the stamp, and contacting at least a portion of the surface with at least a portion of the stamping surface. The stamp can be deformed by compressing it in a plane approximately parallel to the stamping surface, and/or by applying a force to it in a direction approximately perpendicular to the stamping surface.
The present invention also provides a method of making an article, involving etching a pattern into a surface of a template, and molding the article on the surface of the template. This can involve applying to the template a hardenable fluid and allowing the fluid to harden. For example, a prepolymeric fluid can be applied to the template and polymerized. According to one aspect, the hardenable fluid is a fluid precursor of an elastomer. The etching can be anisotropic etching.
The present invention also provides a method of making an article that involves providing a template having a surface anisotropically etched in a pattern, applying a hardenable fluid to the surface, and allowing the fluid to harden.
The present invention also provides a method of patterning a self-assembled monolayer on a nonplanar surface of an article. The method involves rolling the nonplanar surface of the article over a stamping surface of a stamp carrying a self-assembled monolayer-forming molecular species, thereby transferring to the nonplanar surface a self-assembled monolayer of the molecular species. According to one aspect, the rolling step involves applying to the nonplanar surface the self-assembled monolayer in a pattern, while leaving portions of the surface contiguous with the self-assembled monolayer exposed. According to one aspect the exposed portions of the surface are etched.
The present invention also provides a method of making a lens, involving providing a hardenable fluid precursor of the lens, contacting a surface of the fluid precursor with a liquid that is incompatible with the fluid precursor, and allowing the fluid precursor to harden to form a lens. The precursor can be a prepolymeric fluid, and can be a precursor of an elastomer.
The present invention also provides a method of making an article, involving providing a supporting surface having, on a discrete isolated region, a self-assembled monolayer of a molecular species, applying to the self-assembled monolayer a fluid precursor of the article, the precursor having a surface including a first region in contact with the self-assembled monolayer and a second, exposed region contiguous with the first region, contacting the exposed region of the precursor surface with a fluid that is incompatible with the precursor fluid, and allowing the precursor to harden.
The present invention also provides a method of making a diffraction grating, involving coating a surface of a template with a hardenable, fluid diffraction grating precursor, allowing the fluid precursor to harden and form a diffraction grating, and removing the diffraction grating from the template.
The present invention also provides a method of making an optical element, involving molding an article by coating a mold having an optical surface with a hardenable fluid and allowing the fluid to harden to form an article having an optical surface that correlates to the optical surface of the mold, removing the article from the mold, and contacting the optical surface of the article with a liquid metal.
The present invention also provides articles made by the above and other methods, including an article including on its surface an isolated region of a self-assembled monolayer of a molecular species, the isolated region including a lateral dimension of less than 10 microns. Preferably, the dimension is less than 5 microns, more preferably less than 1 micron, more preferably less than 0.5 micron, more preferably less than 0.25 micron, more preferably less than 0.2 micron, more preferably less than 0.15 micron, and most preferably less than 0.1 micron. Also provided is a device including on its surface an pattern of a self-assembled monolayer of a molecular species, the pattern having a lateral dimension of less than 10 microns, or one of the other preferred dimensions above. Also provided is a device including on its surface an pattern of a self-assembled monolayer of a molecular species, the pattern including two closely-spaced regions of a single self-assembled monolayer, or closely-spaced different self-assembled monolayers, the dimension between them being less than 10 microns, or one of the other preferred dimensions above.
The present invention also provides a diffraction grating including a liquid metal having a surface that is in contact with and correlates to a surface of an article. The article surface correlates to an diffraction grating, and the liquid metal surface is formed thereby into a diffraction grating. The grating can be transparent and flexible, preferably transparent and elastomeric.
The present invention also provides an optical element including an elastomer including a void having an optical convex or concave surface, and a liquid metal adjacent the convex or concave surface of the void. Preferably, the liquid metal fills the void and is encapsulated by the elastomer.
The present invention also provides a device including an article defining a surface, a first and a second isolated region of a self-assembled monolayer on the surface, the first and second regions separated from each other by less than 10 microns. Preferably, the separation is one of the preferred dimensions above.
The present invention also provides a device including an article defining a surface, and a self-assembled monolayer on the surface, forming a pattern having a lateral dimension of less than 10 microns. Preferably, the lateral dimension is one of the preferred dimensions above.
The present invention also provides methods utilizing the above and other devices and arrangements, including a method of diffracting electromagnetic radiation. The method involves directing electromagnetic radiation at a liquid metal having a surface that is a diffraction grating to cause diffraction of the electromagnetic radiation, and allowing diffracted electromagnetic radiation to reflect from the surface. The surface of the liquid metal that is a diffraction grating can be deformed (elongated or stretched, bent, compressed, e.g.) to adjust the pattern of diffraction of the electromagnetic radiation.
The present invention also provides a method of focusing electromagnetic radiation, involving directing electromagnetic radiation at a liquid metal having a concave surface, and allowing the electromagnetic radiation to reflect from the surface.
The present invention also provides a method of controlling the shape of a liquid, involving providing a supporting, electrically-conductive surface having, on a discrete isolated region, a self-assembled monolayer of a molecular species exposing a chemical functionality that is compatible with the liquid, positioning the liquid on the self-assembled monolayer of the molecular species, surrounding the liquid with a fluid electrolyte that is not compatible with the liquid, and adjusting an electrical potential of the electrically-conductive surface to control the shape of the liquid.
The present invention also provides a method of printing a self-assembled monolayer on a surface of an article, involving rolling over the surface of the article a nonplanar stamping surface of a stamp carrying a self-assembled monolayer-forming molecular species.